<template>
	<view class="tui-lazyload__box"
		:style="{backgroundColor:placeholder?'transparent':backgroundColor,width:width,borderRadius:radius}"
		@tap="handleClick">
		<image class="tui-lazyload__img"
			:class="{'tui-img__hidden':!placeholder && fadeShow && !show,'tui-img__appear':show && !placeholder && fadeShow}"
			:style="{height:height,borderRadius:radius}" :id="uid" :src="show?src:placeholder" :mode="mode" :webp="webp"
			:show-menu-by-longpress="showMenuByLongpress" :draggable="draggable" @load="load" @error="error">
		</image>
		<slot></slot>
	</view>
</template>

<script>
	export default {
		name: "tui-lazyload-img",
		options: {
			virtualHost: true
		},
		props: {
			//图片路径
			src: {
				type: String,
				default: ''
			},
			//占位图路径
			placeholder: {
				type: String,
				default: ''
			},
			//占位背景色，placeholder有值时失效
			backgroundColor: {
				type: String,
				default: '#E7E7E7'
			},
			//图片的裁剪模式，参考image组件mode属性
			mode: {
				type: String,
				default: 'widthFix'
			},
			//图片显示动画效果,无占位图时有效
			fadeShow: {
				type: Boolean,
				default: true
			},
			//默认不解析 webP 格式，只支持网络资源 微信小程序2.9.0
			webp: {
				type: Boolean,
				default: false
			},
			//开启长按图片显示识别小程序码菜单 微信小程序2.7.0
			showMenuByLongpress: {
				type: Boolean,
				default: false
			},
			//鼠标长按是否能拖动图片 仅H5平台 3.1.1+ 有效
			draggable: {
				type: Boolean,
				default: true
			},
			//图片宽度
			width: {
				type: String,
				default: '340rpx'
			},
			//图片高度，如果高度设置为auto，mode值需要设置为widthFix
			height: {
				type: String,
				default: '340rpx'
			},
			//图片圆角值，如：10rpx
			radius: {
				type: String,
				default: '0'
			},
			//节点布局区域的下边界,目标节点区域以下 bottom(px) 时，就会触发回调函数
			bottom: {
				type: [Number, String],
				default: 50
			},
			//是否停止监听，设置为true时回调函数将不再触发
			disconnect: {
				type: Boolean,
				default: false
			},
			//图片在列表中的索引值
			index: {
				type: Number,
				default: 0
			}
		},
		data() {
			return {
				show: false,
				uid: null
			};
		},
		watch: {
			disconnect(val) {
				if (val) {
					this.removeObserver()
				}
			}
		},
		created() {
			this.observer = null;
			this.uid = this.unique() + this.index;
		},
		mounted() {
			if (!this.disconnect) {
				this.initObserver()
			} else {
				this.show = true;
			}
		},
		beforeDestroy() {
			this.removeObserver()
		},
		methods: {
			unique: function(n) {
				n = n || 6;
				let rnd = '';
				for (let i = 0; i < n; i++)
					rnd += Math.floor(Math.random() * 10);
				return 'tui_' + new Date().getTime() + rnd;
			},
			removeObserver() {
				if (this.observer) {
					this.observer.disconnect()
					this.observer = null;
				}
			},
			initObserver() {
				if (this.observer || this.show) return;
				try {
					let element = this.uid ? `#${this.uid}` : '.tui-lazyload__img';
					const observer = uni.createIntersectionObserver(this)
					observer.relativeToViewport({
						bottom: Number(this.bottom) || 50
					}).observe(element, (res) => {
						if (res.intersectionRatio > 0 && !this.show) {
							this.show = true;
							this.removeObserver()
						}
					})
					this.observer = observer
				} catch (e) {
					//TODO handle the exception
					this.show = true;
					this.removeObserver()
				}
			},
			error(e) {
				if (!this.show) return;
				this.$emit('error', {
					detail: e.detail,
					index: this.index
				})
			},
			load(e) {
				if (!this.show) return;
				this.$emit('load', {
					detail: e.detail,
					index: this.index
				})
			},
			handleClick(e) {
				this.$emit('click', {
					index: this.index
				})
			}
		}
	}
</script>

<style scoped>
	.tui-lazyload__box {
		display: inline-block;
		position: relative;
	}

	.tui-lazyload__img {
		width: 100%;
		display: block;
		flex-shrink: 0;
		transition: opacity .3s linear;
	}

	.tui-img__hidden {
		opacity: 0;
	}

	.tui-img__appear {
		opacity: 1;
	}
</style>
